The Effects of Dietary Nitrate Supplementation on Explosive Exercise Performance: A Systematic Review

Acute inorganic nitrate ingestion does not impact oral microbial composition, cognitive function, or high-intensity exercise performance in female team-sport athletes

The purpose of this study was to investigate the effects of acute nitrate (NO3-)-rich beetroot juice ingestion on explosive and high-intensity exercise performance, oral microbiota composition, and cognitive flexibility (i.e., function), before and after maximal intermittent running exercise. Fifteen women team-sport athletes were assigned in a randomized, double-blind, crossover design to consume concentrated NO3--depleted beetroot juice (PL; 0.1 mmol NO3-) and NO3--rich beetroot juice (BR; 12.0 mmol NO3-) 2.5 h prior to performing a battery of exercise performance tasks and cognitive testing before and after the Yo-Yo intermittent recovery level 1 (YYIR1) running test. Resting plasma [NO3-] and plasma nitrite ([NO2-]) were elevated following BR (P < 0.001). BR did not impact global composition or relative abundance of taxa in the oral microbiome (P > 0.05) or cognitive flexibility before or after exercise (P > 0.05). There was no significant difference in performance during 20-m (PRE, PL: 4.38 ± 0.27 vs. BR: 4.38 ± 0.32 s; POST, PL: 4.45 ± 0.29 vs. BR: 4.43 ± 0.35 s) and 10-m sprints (PRE, PL 2.78 ± 0.15 vs. BR 2.79 ± 0.18 s; POST, PL: 2.82 ± 0.16 vs. BR: 2.81 ± 0.19 s), isokinetic handgrip dynamometry, medicine ball throw, horizontal countermovement jump, or YYIR1 (PL: 355 ± 163 m vs. BR: 368 ± 184 m) between BR and PL (P > 0.05). These findings indicate that acute dietary NO3- may not influence the oral microbiome, explosive and high-intensity exercise performance, or cognitive function in women team-sport athletes.

The Cardioprotective Role of Nitrate-Rich Vegetables

Nitric oxide (NO) is an inorganic radical produced by both the non-enzymatic nitrate (NO3-)-nitrite (NO2-)-NO pathway and enzymatic reactions catalyzed by nitric oxide synthase (NOS). Also, as nitrate and nitrite from dietary and other endogenous sources can be reduced back to nitric oxide in vivo, the endogenous NO level can be increased through the consumption of nitrate-rich vegetables. Ingestion of dietary NO3- has beneficial effects which have been attributed to a subsequent increase in NO: a signaling molecule that may regulate various systems, including the cardiovascular system. A diet rich in NO3- from green leafy and root vegetables has cardioprotective effects, with beetroot products being particularly good sources of NO3-. For example, various studies have demonstrated a significant increase in nitrite levels (regarded as markers of NO) in plasma after the intake of beetroot juice. The present review describes the current literature concerning the role of nitrate-rich vegetables (especially beetroot products) in the prophylaxis and treatment of cardiovascular diseases (CVDs). This review is based on studies identified in electronic databases, including PubMed, ScienceDirect, Web of Knowledge, Sci Finder, Web of Science, and SCOPUS.

Does Co-Supplementation with Beetroot Juice and Other Nutritional Supplements Positively Impact Sports Performance?: A Systematic Review

In the pursuit of enhanced athletic prowess in different disciplines, athletes constantly look for strategies to increase their physical performance, encompassing technical skills and dietary components, which inevitably, in most cases, include the incorporation of sports supplements. In recent years, there has been an increase in the number of athletes using ergogenic aids. In this context, scientific evidence must play a prominent role in either endorsing or warning against the use of these products, ensuring the preservation of health while promoting the theoretically established positive benefits. In this vein, beetroot juice (BJ) stands out as a key supplement as an ergogenic aid to improve sports performance, given its demonstrated influence on both aerobic and anaerobic exercise. However, despite widespread global demand, there remains a lack of understanding regarding the potential synergistic effects of combining BJ with other supplements. Consequently, our study aims to determine whether the combination of BJ with another nutritional supplement can enhance its beneficial effects and, therefore, optimize physical performance in humans. A comprehensive literature search was conducted in two major databases-Web of Science and PubMed-from 1 January 2018 to 29 January 2023, using specific keywords. After the exclusion criteria, six articles were selected for analysis. Therefore, our study shows that the effectiveness of combining BJ with another supplement mainly depends on the duration of the chronic intervention, which is where the greatest benefits have been observed.

Supplementation with Nitric Oxide Precursors for Strength Performance: A Review of the Current Literature

Nitric-oxide-stimulating dietary supplements are widely available and marketed to strength athletes and weightlifters seeking to increase muscle performance and augment training adaptations. These supplements contain ingredients classified as nitric oxide (NO) precursors (i.e., "NO boosters"). Endogenous NO is generated via a nitric oxide synthase (NOS)-dependent pathway and a NOS-independent pathway that rely on precursors including L-arginine and nitrates, with L-citrulline serving as an effective precursor of L-arginine. Nitric oxide plays a critical role in endothelial function, promoting relaxation of vascular smooth muscle and subsequent dilation which may favorably impact blood flow and augment mechanisms contributing to skeletal muscle performance, hypertrophy, and strength adaptations. The aim of this review is to describe the NO production pathways and summarize the current literature on the effects of supplementation with NO precursors for strength and power performance. The information will allow for an informed decision when considering the use of L-arginine, L-citrulline, and nitrates to improve muscular function by increasing NO bioavailability.

Does Beetroot Supplementation Improve Performance in Combat Sports Athletes? A Systematic Review of Randomized Controlled Trials

While studies on dietary nitrate (NO₃^-) supplementation and its impact on combat sports performance are increasing, finite conclusions from currently available investigations remain unclear. Thus, the present systematic review examined the acute and chronic ergogenic effect(s) of dietary nitrate intake from beetroot on different aspects of combat sports performance. A systematic search for randomized placebo-controlled studies investigating the effects of beetroot supplementation on combat sports outcomes was performed through Scopus, PubMed/MEDLINE, Web of Science, Scielo, Sport Discus, and Cochrane Library databases up to 2 January 2023. The different terms related to beetroot and to combat sports were connected in the search strategies using the Boolean operators 'AND' and 'OR'. A total of nine studies with good methodological quality (based on the Cochrane risk of bias tool) fulfilled the inclusion criteria. Seven studies used an acute supplementation strategy, while the other two studies utilized chronic supplementation. Findings showed beetroot intake may be an effective tool to improve oxidative metabolism and muscle force production (i.e., isokinetic and isometric) in combat sports athletes. However, these effects may depend on the population, intake duration, muscle group activated, and exercise type. Future studies are required to (1) understand the effects on female athletes and (2) elucidate the impacts of dosing protocols and specific exercise modalities for enhancing combat sports performance.

Influence of Beetroot Juice Ingestion on Neuromuscular Performance on Semi-Professional Female Rugby Players: A Randomized, Double-Blind, Placebo-Controlled Study

PURPOSE

Beetroot juice (BRJ) is considered an ergogenic aid with good to strong evidence for improving human performance in sport modalities with similar demands to rugby. However, most of the studies were realized in male athletes with limited evidence in female athletes. Thus, the aim of this study was to explore the acute ingestion of BRJ in female rugby players.

METHODS

Fourteen semi-professional female rugby players (25.0 ± 3.7 years) belonging to a team from the First Spanish Female Rugby Division participated in this study. Participants were randomly divided into two groups that realized a neuromuscular battery after BRJ (140mL, 12.8 mmol NO₃^-) or placebo (PLAC, 140 mL, 0.08 mmol NO₃^-) ingestion on two different days separated by one week between protocols. The neuromuscular test battery consisted of a countermovement jump (CMJ), isometric handgrip strength (i.e., dominant), 10-m and 30-m sprint, agility t-test and Bronco test. Afterwards, participants reported a rate of perception scale (6-20 points) and side effects questionnaire associated with BRJ or PLAC ingestion.

RESULTS

Statistically significant improvements were observed in CMJ (7.7%; p = 0.029; ES = 0.62), while no differences were reported in dominant isometric handgrip strength (-1.7%; p = 0.274; ES = -0.20); 10-m and 30-m sprint (0.5-0.8%; p = 0.441-0.588; ES = 0.03-0.18); modified agility t-test (-0.6%; p = 0.503; ES = -0.12) and Bronco test (1.94%; p = 0.459; ES = 0.16).

CONCLUSIONS

BRJ ingestion could improve neuromuscular performance in the CMJ test, while no differences in sprint (10-m and 30-m sprint test), agility, isometric handgrip strength and endurance performance (i.e., Bronco test) were reported.

The effects of nitrate ingestion on high-intensity endurance time-trial performance: A systematic review and meta-analysis

Background/Objective

Dietary nitrate ingestion extends endurance capacity, but data supporting endurance time-trial performance are unclear. This systematic review and meta-analysis evaluated the evidence for dietary nitrate supplementation to improve high-intensity endurance time-trial performance over 5–30 min on the premise that nitrate may alleviate peripheral fatigue over shorter durations.

Methods

A systematic literature search and data extraction was carried out following PRISMA guidelines and the PICOS framework within five databases: PubMed, ProQuest, ScienceDirect, Scopus and SPORTDiscus. Search terms used were: (nitrate OR nitrite OR beetroot) AND (high intensity OR all out) AND (time trial or total work done) AND performance.

Results

Twenty-four studies were included. Fifteen studies applied an acute supplementation strategy (4.1 mmol–15.2 mmol serving on one day), eight chronic supplementation (4.0 mmol–13.0 mmol per day over 3–15 days), and one applied both acute and chronic supplementation (8.0 mmol on one day and over 15 days). Standardised mean difference for time-trial ranging from 5 to 30 min showed an overall trivial effect in favour of nitrate (Hedges'g = 0.15, 95% CI -0.00 to 0.31, Z = 1.95, p = 0.05). Subgroup analysis revealed a small, borderline effect in favour of chronic nitrate intervention (Hedges'g = 0.30, 95% CI -0.00 to 0.59, Z = 1.94, p = 0.05), and a non-significant effect for acute nitrate intervention (Hedges'g = 0.10, 95% CI -0.08 to 0.28, Z = 1.11, p = 0.27).

Conclusion

Chronic nitrate supplementation improves time-trial performance ranging from 5 to 30 min.

Bioavailability, Efficacy, Safety, and Regulatory Status of Creatine and Related Compounds: A Critical Review

In 2011, we published a paper providing an overview about the bioavailability, efficacy, and regulatory status of creatine monohydrate (CrM), as well as other “novel forms” of creatine that were being marketed at the time. This paper concluded that no other purported form of creatine had been shown to be a more effective source of creatine than CrM, and that CrM was recognized by international regulatory authorities as safe for use in dietary supplements. Moreover, that most purported “forms” of creatine that were being marketed at the time were either less bioavailable, less effective, more expensive, and/or not sufficiently studied in terms of safety and/or efficacy. We also provided examples of several “forms” of creatine that were being marketed that were not bioavailable sources of creatine or less effective than CrM in comparative effectiveness trials. We had hoped that this paper would encourage supplement manufacturers to use CrM in dietary supplements given the overwhelming efficacy and safety profile. Alternatively, encourage them to conduct research to show their purported “form” of creatine was a bioavailable, effective, and safe source of creatine before making unsubstantiated claims of greater efficacy and/or safety than CrM. Unfortunately, unsupported misrepresentations about the effectiveness and safety of various “forms” of creatine have continued. The purpose of this critical review is to: (1) provide an overview of the physiochemical properties, bioavailability, and safety of CrM; (2) describe the data needed to substantiate claims that a “novel form” of creatine is a bioavailable, effective, and safe source of creatine; (3) examine whether other marketed sources of creatine are more effective sources of creatine than CrM; (4) provide an update about the regulatory status of CrM and other purported sources of creatine sold as dietary supplements; and (5) provide guidance regarding the type of research needed to validate that a purported “new form” of creatine is a bioavailable, effective and safe source of creatine for dietary supplements. Based on this analysis, we categorized forms of creatine that are being sold as dietary supplements as either having strong, some, or no evidence of bioavailability and safety. As will be seen, CrM continues to be the only source of creatine that has substantial evidence to support bioavailability, efficacy, and safety. Additionally, CrM is the source of creatine recommended explicitly by professional societies and organizations and approved for use in global markets as a dietary ingredient or food additive.